Should I use 400 or 600 grit on my CFX chamber?

[fisherdude]

My CFX came with a bad seal on the end of the piston which is why I don't think the accuracy is quite what it should have been   It was apparently sliced by burrs during assembly.  I have it torn down to replace the seal and I am of course I wil deburr.  Should I touch up the compression chamber with 400 or 600 grit or just leave it the way it is as it looks OK?

Ron Alexander

[shootist]

Use the 600 grit. You don't want the bigger scratches the 400 would leave. Good luck - Lee

[shootist]

Hope you have put a GRT-lll trigger in already. It will be the best money you ever spent on your air rifle. It makes a huge difference. That and a tune, you'll have a very different gun. Lee

[preez]

You DO WANT the scratches in! That's where the lube will be! 400 and 600 are too fine for compression chamber. What you need to do is hone it with 200-220 grit in a cross hatch pattern. Do a search on this forum.

Chris

[daved]

CDT did the comp tubes with a 320 grit hone.  When I did my CFX I went to 400, because I was installing a gas ram, but for the last inch or so, where the rotary rides, I went as fine as I could, 1500 wet/dry.  My reasoning was, you DON'T want lube getting past the oring, and my understanding is that the finer the surface, the better for an oring seal.  Seemed to work, I'd been having sealing problems with that rifle and that seemed to fix it.  LOTS of WD-40 for cutting lube and cleaner, blast out excess with compressed air, then clean with LOTS of brake cleaner, then blast again.  Used silicone dielectric grease to lube the oring when I reinstalled the rotary, then moly for the piston seal and piston per CDT and JM.  No other lubes in that case, of course, like I said, I was installing a Theoben gas ram.  Hope that helps.

Dave

[fisherdude]

It makes sense to me that there should be "some" place for lube to hold.  My brake hone is about 220 grit and I know from my machine shop class that the speed I run it at also has some bearing on the finish - faster = finer.  My CFX uses a synthetic seal, if it were leather, I would probably just leave it with the brake hone's 220 grit finish.  I could also just keave it the way Gamo finished it.  Any other opinions?

Ron Alexander

[shootist]

Hey Chris,  don't know how many tunes you've done, but if you use 220, you'll be going thru piston seals in a hurry.  I special ordered 400 grit stones and then hone further w/600 grit to smooth it out.Lee

[preez]

I've done 3 springer tunes on a Big Cat, CFX, and B-26. I used Maccari seals and lubes on all 3 of them. No problems with any of them "going through the seals"

I did my tunes according to a write-up by Charlie Da Tuna, in which he clearly states that high polish (400-600 grit) is for leather seals and should not be applied for synthetic seals. You're not suppose to really dig into the metal with sandpaper/hone, just give it a nice cross hatch.

But than again, I might be wrong, it wouldn't be the first time... ;)

Chris

P.S. The only springer I kept is the B26. Amazingly it gets consistant 680 fps in .22 with very little variations

[shootist]

I may be wrong, but if you read CDT tune up guide, he goes 400 grit. I special ordered 400 grit stones for my brake hone. Then I go over it w/600 grit. It works very well. I've done about 100-120 rifle tunes. I have guys that are shooting 150-200 pellets a day. So far so good. When I first started doing it, if the person didn't have a lot of money, I'd put the old spring back in if it wasn't too bad. Just had one of those come back with a broken spring a year later. The spring was 29 years old in an RWS. CDT and I don't agree on all things, but I still tune guns by his guide. It is a reliable resource. As far as materials go, JM is my only source. Lee

[preez]

You made me doubt myself... ;)  I had to go back to my trusty printout of Charlie's guide. I am sticking with the 220 cause that's what the man said! LOL

Seriously though, I remember not being able to get 3 stone hone in 220 grit, they only came in 320 in my car parts store. I did my first tune with that hone and soapy water, for my next tunes I made a hone out of wooden dowels and fed it 220 grit paper with similar results.

There's more than 1 way to skin a cat (or a squirrel)

Chris

[70GTvert]

220 is fine if done at low power or by hand. 1500, well that is one selection short of a base coat clear coat final sand on the clear in automotive use. In fact, I have seen people end up with an award winning gloss using 1000 on their auto. Metal is tougher than paint or plastic. If this were anything short of metal, perhaps finer than 220 would be sufficent. Also, how is it being finished? Machine or hand? More material will be removed with any grit if machined. Anything much heavier and yes, you will start having some issues, Over time, even that seal will start to polish down those walls.

[CharlieDaTuna]

Actually in my opinion, you should use 400 grit in a springer with a synthetic seal. 200 grit is to course and although wear won't be that significant due to the excessive lube that it gets but more importantly, it allows too much lube to get by the seal causing excessive combustion and possibly even detonation in the compression chamber.  Using 600 grit is way too fine and should be used with guns utilizing a leather seal. 600 grit will usually cause fuel/lube deprivation causing lower and quit often erratic velocities  and will allow little seal lubrication. That in turn allows the piston to slam home harder creating a harsher firing cycle.

[mikeiniowa]

I have had one or two rifles taken in trade that had the chambers done in a very rough grit, both ate the seals in 100 shots or less, it was hard to tell with all the lube getting by but when I took them apart the seals were very loose and you could see where they had worn down, stick with 400 or so......

[CharlieDaTuna]

Yes, what Mike says is very likely. What usually happens, especially with the Chinese or similar seals is when the lube gets by the seal and you have ongoing detonation, the seal will get very hard and the edges even begin to crystallize. Then it doesn't take long at all for the seal to wear. The older B-21's and even the B-30's had a history of actually burning out one side of the seal.... burn a hole right through it.

As an example, here are three pics so that one can see just what incorrect lubes or incorrectly installed seal results can be.  The light colored seal is out of a B-21 with less than 20 shots through it. The dark seal is out of a Gamo Shadow 1000. You can see on the Shadow in particular how it is burnt and crystallized it is. Also, take notice of the steel particles imbedded in the seals. All of the speckles in the B-21 seal where the burnt out section is mostly reflection from the flash.

 The Gamo was using Kodiak's. Heavy pellets are not good especially if you have a leaking seal and incorrect lubes. In addition to the seal being destroyed, the spring was broken in two places and the spring block was cracked.

[shadow]

YIKES!!!!!!!! perfect examples Bob. Ed